Mohammad ,

The quick answer is that I would not recommend using Workflow to import documents, especially from an FTP site.  If you have access to the Laserfiche SDK then a stand-alone service based integration similar to Import Agent would be a much more robust and scalable solution than anything you could build through Workflow.  As a Laserfiche PDP (Professional Developer Partner) we could certainly assist you in developing this type of integration.

All that being said; as an academic exercise this could be accomplished through Workflow.  To your specific question; there would be no initial advantage to building a custom workflow activity versus coding up something in an SDK script activity.  Coding in a script activity is much more straight-forward than building a custom workflow activity. 

If I had to use Workflow to do this I would create the new document and assign metadata using existing workflow activities and I would reference the new document in the SDK script activity to import pages into that document from the FTP site/folder.  The SDK script activity would be responsible for connecting and authenticating to the FTP site/folder, retrieving a list of images, importing those images as new pages in the document, then deleting (or moving) the source images from the FTP site. 

You would also have to code around whether or not you would import only images as Laserfiche pages or also handle importing electronic documents as attachments.

Some things to keep in mind;

• Depending on how you trigger and monitor your workflow you could have multiple instances running concurrently trying to access the FTP site importing the same images into multiple documents.
• Importing documents is a resource intensive process so running this process on a production workflow server would assuredly have a negative impact on its performance.
• In the SDK Script activity itself you would need to include a reference to Laserfiche.DocumentServices.DocumentImporter to gain access to the ImportImages and/or the ImportEdoc methods.